H. Di Benedetto

Influence of reclaimed asphalt pavement content on complex modulus of asphalt binder blends and corresponding mixes: experimental results and modelling

The objective of the presented study is to determine linear viscoelastic (LVE) properties of corresponding binders and mixes and to check how they change with reclaimed asphalt pavement (RAP) content. The investigation is part of a wider on-going research project, in the framework of a PhD thesis, in collaboration between Université de Lyon/École Nationale Travaux Publics de l’État (ENTPE), EIFFAGE Travaux Publics and Beyond Petroleum. Dynamic shear rheometer and tension/compression (using a Métravib device) complex modulus tests were performed on nine different bitumens, produced as blends of two different base bitumens and RAP-extracted bitumen in various proportions. LVE properties of six asphalt mixes, produced with the same materials and proportions of certain bitumen blends among the nine tested ones, were measured in tension/compression mode. 2 Springs, 2 Parabolic Elements, 1 Dashpot model was used to fit experimental data both for binders and mixes. Shift-Homothety-Shift in time-Shift transformation (developed at ENTPE) was applied to verify the correspondence of LVE behaviours of related binders and mixes.

Assessment of Existing Micro-mechanical Models for Asphalt Mastics Considering Viscoelastic Effects

ABSTRACT Micromechanical models have been directly used to predict the effective complex modulus of asphalt mastics from the mechanical properties of their constituents. Because the micromechanics models traditionally employed have been based on elastic theory, the viscoelastic effects of binders have not been considered. Moreover, due to the unique features of asphalt mastics such as high concentration and irregular shape of filler particles, some micromechanical models may not be suitable. A comprehensive investigation of four existing micromechanical methods is conducted considering viscoelastic effects. It is observed that the self-consistent model well predicts the experimental results without introducing any calibration; whereas the Mori-Tanaka model and the generalized self-consistent model, which have been widely used for asphalt materials, significantly underestimate the complex Youngs modulus. Assuming binders to be incompressible and fillers to be rigid, the dilute model and the self-consistent model provide the same prediction, but they considerably overestimate the complex Youngs modulus. The analyses suggest that these conventional assumptions are invalid for asphalt mastics at low temperatures and high frequencies. In addition, contradictory to the assumption of the previous elastic model, it is found that the phase angle of binders produces considerable effects on the absolute value of the complex modulus of mastics.

Quantification of biasing effects during fatigue tests on asphalt mixes: non-linearity, self-heating and thixotropy

Various phenomena other than fatigue (so-called “biasing effects”) occur during laboratory fatigue tests on asphalt mixes because of cyclic loading applications, thus altering experimental results and leading to misleading conclusions. The purpose of the study is to isolate and quantify biasing effects, therefore isolating real fatigue damage. In particular, non-linearity, self-heating and thixotropy (defined as a recoverable viscosity reduction after shear application) were evaluated. Six different mixes were produced using three distinct asphalt binders. Tests were performed in tension/compression mode on cylindrical samples. A particular test procedure was followed, consisting of two parts. In the first part, complex modulus measurements were performed at temperatures from 8°C to 14°C and strain amplitudes from 50 to 110 µm/m, at 10 Hz. Regression equations were fitted in order to evaluate variations of norm of complex modulus and phase angle caused by temperature and strain-level changes around common fatigue test conditions (10°C, 100 µm/m). In the second part of the test, five partial fatigue tests (each one consisting of 100,000 cycles at a 100 µm/m strain amplitude) were performed at 10°C, 10 Hz. After each fatigue lag, a 24 hour rest period was imposed. During rest periods, short complex modulus measurements were performed (10°C, 10 Hz) in order to monitor the recovery of mechanical properties. Surface and internal temperature of samples were constantly measured throughout the entire test, in order to monitor self-heating due to repeated loading. A significant temperature increase was observed during each fatigue lag, while, during rest periods, temperature rapidly decreased to the initial value. Self-heating was observed to be correlated to viscoelastic energy dissipation. The procedure used in the study allowed quantitatively estimating biasing effects. Therefore, unrecovered mechanical properties, due to damage accumulation, were obtained. Ninety per cent of total complex modulus and phase angle variations observed during each fatigue lag were found to be completely reversible. Non-linearity and thixotropy appear to influence mechanical properties variations more importantly than self-heating.

Low-Temperature Cracking of Recycled Asphalt Mixtures

The thermo-mechanical behavior of asphalt mixtures, with Recycled Asphalt Pavement (RAP) and other recycled materials was investigated. The cracking behavior at low temperature was studied considering Thermal Stress Restrained Specimen Tests (TSRST). The experimental setup was improved as the radial strains were measured during the performed TSRST. Tri-dimensional behavior could thus be investigated. Mixes made with different RAP content (up to 25%) and manufacturing-waste asphalt roofing shingle content (up to 10%) were studied. The influence of the content of RAP and shingle was analysed. A ranking of the different mixes was proposed based on the classical TSRST outputs, stress and temperature at failure.

Evaluation of pavement materials containing RAP aggregates and hydraulic binder for heavy traffic pavement

Treatment with hydraulic binder is one of the techniques for recycling of reclaimed asphalt pavement (RAP) recovered from road deconstruction. The combined presence of hydraulic binder and bituminous binder (from the RAP) in the mix makes it a composite material, on which the feedback from real road networks is still limited today and which has not yet been considered in the French rational pavement design method (RPDM). The addition of steel fibres in the composite mix allows minimising crack width, solution adopted by the steel fibre-reinforced roller-compacted concrete (FRCC™) technique. FRCC™ mixes with different fibres and RAP contents are compared with another RAP-based material treated with hydraulic binder, ERTALH®. The study discussed in this paper is part of the French National Research Agency project “Recyroute” which aims to evaluate the use of these composite materials in the base layer of heavy traffic roads. Mechanical properties of these composites were investigated by an extensive laboratory test programme. Performance of full-scale pavements was also evaluated throughout an accelerated pavement test (APT). This paper presents the main features and results of the laboratory test programme and the APT experiment as well, leading to propose design parameters of these innovative pavement structures, according to the French RPDM.

Fatigue investigation of mastics and bitumens using annular shear rheometer prototype equipped with wave propagation system

A research project on fatigue behavior of bitumens and mastics is developed at University of Lyon, ENTPE/DGCB in collaboration with TOTAL Company. An innovative device, the Annular Shear Rheometer (ASR), is used to perform advanced experimental investigation. It allows practicing fatigue tests, which could be considered as homogenous, on larger scale specimen than traditional other devices. This apparatus allows measuring the linear viscoelastic (LVE) shear complex modulus (G*) of bituminous materials for small strain amplitudes, and the non linear modulus Ge* for higher strain levels applied during fatigue tests.

Three-Dimensional Characterisation of Linear Viscoelastic Properties of Bituminous Mixtures

This chapter focuses on the three-dimensional linear viscoelastic (3D-LVE) behaviour of bituminous mixtures and in particular on the measurement and modelling of the complex Young’s modulus and Poisson’s ratio (PR). In the first part of the chapter, the LVE definition of PR is reviewed and experimental measurements of the LVE PR carried out over the last 40 years are summarised. The second part of the chapter is devoted to the description of a RILEM round robin test (RRT) organized by Task Group 3 (TG3) “Mechanical testing of bituminous mixtures” of RILEM TC 237-SIB. Within the RRT uniaxial cyclic (sinusoidal tension/compression or haversine compression) tests at different temperatures and frequencies were carried out on cylindrical specimens cored from laboratory compacted slabs. Two types of bituminous mixtures, GB3 (continuously graded) and GB5® (gap-graded), were analysed. Five laboratories participated in the RRT, each laboratory measured axial and transverse (or diametral) strains using different sensors and configurations. In particular, transverse strain was measured along two orthogonal directions in order to evaluate the effect of compaction-induced anisotropy on PR. Results confirmed that PR of bituminous mixtures is a complex function of temperature and frequency and that the time-temperature superposition principle can be applied (for absolute value and phase angle). For the studied mixtures the norm of the complex PR ranged between 0.22 (low temperatures/high frequencies) and 0.60 (high temperatures/low frequencies) whereas the phase angle was less than 6°. A small difference (less than 0.05) was found between measurements carried out in two orthogonal directions. This small difference is probably related to measurement accuracy and not to the anisotropic behaviour of the material. Comparison of data between the different laboratories, which could not be performed at exactly the same temperatures and frequencies, was performed using a common reference given by the 3-dimensional formulation of the 2S2P1D linear viscoelastic model. This model provides a good simulation of experimental data. Based on close results from all participating laboratories, it is possible to conclude that cyclic uniaxial test could be a good candidate to become a standard test for evaluating the 3D-LVE behaviour of bituminous mixtures.

Tridimensional linear viscoelastic behavior of bituminous materials

This chapter gives some insight on recent research focused on the linear viscoelastic (LVE) behavior of bituminous materials. The development of new experimental devices and methods, including evaluation of Poisson’s ratio and wave propagation tests, are described. Three-dimensional (3D) LVE behavior has been investigated, and some results of complex Poisson’s ratio are presented. The time–temperature superposition principle is extended to the 3D case. Results concerning anisotropy are also shown. With a better knowledge of LVE behavior, more adapted analytical models can be developed to fit experimental measurements. The 3D version of the two springs, two parabolic elements, one dashpot (2S2P1D) model is presented, and its capability to capture the behavior of different bituminous materials is highlighted. A method to determine the 3D LVE behavior of mixtures from the LVE behavior of binders, based on a mechanistic approach, is also explained. In the end, this chapter aims to show that bituminous materials can be more precisely characterized.

Fatigue Cracking in Bituminous Mixture Using Four Point Bending Test

This paper describes investigation into cracking in bituminous mixture using the four point bending notched fracture (FPBNF) test, which has been developed at the University of Lyon/ Ecole Nationale de Travaux Publics de l’Etat (ENTPE). A special loading path is applied on the notched beam specimen at a constant temperature of - 4.5°C. A monotonic loading was first applied until the peak load and after unloading, many loading/unloading cycles at small amplitude were carried out until the final failure of specimen. Deflection of the beam and crack mouth opening displacement (CMOD) are measured. Crack length is determined experimentally using crack propagation gauges. It is also obtained with an improved method, called Displacement Ratio Crack length (DRCL) method, developed at ENTPE laboratory, which allows back calculating the crack length. This method is based on the relation between two experimental displacement measurements: the crack mouth opening displacement (CMOD) and the deflection of the beam. The results obtained from this method are discussed and compared with the crack length measured with crack propagation gauges. During the test, the fracture behaviour is investigated. The crack propagation is studied as a function of loading/unloading cycle number. The stress intensity factor is evaluated. Two different domains of crack evolution are distinguished: the first domain where pre-existing crack progressively re-opens, the second domain where crack propagates. The Paris fatigue law could be applied in the domain where crack propagates.